Method for producing halogen-free reactive polyisobutene

ABSTRACT

A process for preparing halogen-free, reactive polyisobutene having a terminal double bond content of more than 50 mol % and an average molecular weight M n  of 280-10000 dalton by the cationic polymerization in the liquid phase of isobutene or hydrocarbon mixtures comprising isobutene comprises polymerizing at from −30° C. to +40° C. in the presence of a heterogeneous polymerisation catalyst comprising one or more oxides of the elements of transition groups V and VI of the Periodic Table of the Elements or in the presence of a heterogeneous polymerization catalyst comprising one or more oxidic compounds of one or more elements of transition groups V and VI of the Periodic Table of the Elements supported on a non-zeolitic oxidic support material which is not an oxygen-containing zirconium compound, the catalyst not containing a technically effective amount of halogen.

The present invention relates to a process for preparing halogen-free,reactive polyisobutene;having a terminal double bond content of morethan 50 mol % and an average molecular weight A M_(n) of 280-10000dalton by the cationic polymerization in the liquid phase of isobuteneor hydrocarbon mixtures containing the isobutene.

The polymerization of isobutene yields an inseparable mixture ofpolyisobutenes, in which the position of the double bond varies betweenthe individual polyisobutenes. Polyisobutenes of formula

wherein n is the degree of polymerization which in turn is derived fromthe average molecular weight M_(n) of the polyisobutene prepared,contain terminal C—C double bonds of the vinylidene type which areherein also referred to as α-olefinic double bonds owing to theirposition in the polyisobutene molecule. Accordingly, the double bonds inpolyisobutenes of formula II

are referred to as β-olefinic. If the polymerization of isobutene iscarried out without taking special measures, a random mixture is formedwhich comprises polyisobutenes having α-olefinic, i.e. terminal, doublebonds, β-olefinic double bonds and double bonds located further towardthe interior of the polyisobutene molecule. The terminal double bondcontent and the β-olefinic double bond content of a polyisobuteneproduct prepared by a particular process are both reported in mol %.

Polyisobutenes having molecular weights of up to 100000 dalton areknown. These olefins are usually prepared by Lewis acid-catalyzedisobutene polymerization employing aluminum chloride, alkylaluminumchloride or boron trifluoride as Lewis acids, as described, for example,in H. Guterbock, Polyisobutylene und Mischpolymerizate, p. 77-104,Springer Verlag, Berlin, 1959. However, the resulting polymers have arelatively low vinylidene type terminal C—C double bond content of lessthan 10 mol %.

In contrast, reactive polyisobutene (PIB) having molecular weights ofusually 500-5000 dalton has a high terminal vinylidene group content of,preferably, more than 50 mol %. These reactive polyisobutenes are usedas intermediates in the preparation of lubricant and motor fueladditives as described, for example, in DE-A 27 02 604 (see U.S. Pat.No. 4,152,499). These additives are prepared by initially reactingpolyisobutene with maleic anhydride. The preferred reactive sites forthis reaction are the terminal double bonds of the vinylidene type,whereas double bonds located further toward the interior of themacromolecule react to a lesser extent if at all, depending on theirposition in the molecule. The polyisobutene/maleic anhydride adductsformed are then reacted with certain amines to give the correspondingadditives. It is therefore absolutely necessary for polyisobutenes usedas starting materials for the abovementioned additives to have a highterminal double bond content. The same applies to the preparation of thepolyisobuteneamines of EP-A 244 616 (see U.S. Pat. No. 4,832,702) whichare also used as motor fuel additives and which are prepared byhydroformylation of the reactive polyisobutene and subsequent reductiveamination of the resulting polyisobutene aldehyde. For this process,preference is likewise given to using polyisobutene having a highterminal double bond content, but β-olefinic polyisobutenes also givethe desired product when the hydroformylation is carried out usingcobalt catalysts, owing to their double bond isomerization activity.

The preparation of reactive polyisobutene by homogeneously catalyzedpolymerization of isobutene is already known. According to DE-A 27 02604, for example, a polyisobutene product having a terminal double bondcontent of up to 88% is obtained by reacting isobutene in the presenceof boron trifluoride. EP-A 145 235 (see U.S. Pat. No. 4,605,808) teachesthe polymerization of isobutene in the presence of a complex of borontrifluoride and a primary alcohol at from −100° C. to +50° C. to giveproducts with similarly high vinylidene double bond contents. Accordingto U.S. Pat. No. 5,286,823, highly reactive polyisobutene can also beprepared using complexes of boron trifluoride and secondary alcohols ascatalysts.

The disadvantages of this homogeneously catalyzed process are that theLewis acid catalysts used are corrosive and that there is a risk that,apart from the desired reactive polyisobutene, halogenated polymericbyproducts are formed which are virtually inseparable from PIB andadversely affect the product and processing characteristics of the PIB.In these processes, the homogeneous catalyst is usually separated byquenching with a nucleophile to destroy the catalyst and subsequentlyremoving the PIB from the quenching mixture by extraction. Theseadditional workup steps are a further disadvantage of the homogeneouslycatalyzed PIB preparation process.

WO 94/28036 discloses, inter alia, the preparation of polyisobuteneusing heterogeneous Lewis acid-like catalysts.

Catalysts used are salts of elements of transition groups III, IV, V andVI of the Periodic Table of the Elements, which salts are insoluble inthe reaction medium, preferably halides, sulfates, perchlorates,trifluoromethanesulfonates, nitrates and fluorosulfonates thereof. Inthe examples of this application, only the halides of these elements areused as catalysts for isobutene polymerization. No information is givenabout the properties of the polyisobutene obtained in these examples interms of their molecular weight or their terminal double bond content.The polymerization is terminated by adding methanolic ammonia solutionto the reaction medium to destroy or at least substantially inactivatethe catalysts in question.

The preparation of PIB using heterogeneous catalysts is also known. U.S.Pat. No. 4,288,649 describes a process for preparing polyisobutenehaving an average molecular weight of >1250 dalton by polymerizing C₄hydrocarbon mixtures comprising isobutene over halided aluminacatalysts. These catalysts are prepared by treating the alumina with ahaliding agent, preferably with a chloriding agent, in particular withcarbon tetrachloride, at an elevated temperature. The disadvantage ofthis process is that some of the chlorine is transferred from thecatalyst to the polymer which forms. For example, the polymerization ofa mixture of n-butane, isobutane and isobutene over a chlorided aluminacatalyst prepared in this manner gives, after a reaction time of 2hours, a polyisobutene product having a chlorine content of 46 ppm.

U.S. Pat. No. 5,326,920 discloses a process for polymerizing isobuteneby employing as heterogeneous catalyst an oxidic support material,preferably silica, which has been activated with a metal chlorideattached thereto, preferably with an aluminum chloride. Particularpreference is given therein to an SiO₂—AlCl₂ catalyst in which AlCl₂groups are anchored on the SiO₂ support via oxygen linkages. Thedisadvantages of this process are that the polyisobutene productsobtained have an extremely broad molecular weight distribution D of from8 to 14, a low terminal double bond content and a chlorine content inthe ppm range. Furthermore, this process requires the presence ofpromoters such as water, alcohols, alkyl halides or hydrogen chloride toachieve a catalyst activity which is sufficient for industrialoperation. Similar catalyst systems for the polymerization of isobuteneare described in WO 95/26815, WO 95/26816, WO 95/26814 and WO 96/26818.

JP-A 139 429/1981 utilizes heterogeneous zirconium dioxide andmolybdenum oxide catalysts to prepare isobutene oligomers having amolecular weight of less than 300 dalton. These catalysts can be mixedwith aluminum fluoride to increase their activity. According to thispublication, the reaction of an isobutene-comprising C₄ cut(composition: 46% of isobutene, 28% of 1-butene, 8% of 2-butenes, 12% ofn-butane, 5% of isobutane, 1% of 1,3-butadiene) over an MoO₃/ZrO₂catalyst having a molybdenum content, calculated as MoO₃, of 13% byweight at 120° C. yields an isobutene oligomer mixture comprising 29% ofdiisobutene, 49% of triisobutene and 19% of tetraisobutene.

NL-A 7 002 055 discloses a process for preparing isobutene oligomers inthe gas phase using a tin oxide/molybdenum oxide on silica catalyst togive a mixture of isobutene dimers, trimers and tetramers.

EP-A 535 516 (see U.S. Pat. No. 5,310,712) discloses a catalyst for thepreparation of ethylene polymers comprising chromium trioxide on aparticular SiO₂ support material. This publication does not teach thepreparation of reactive, low molecular weight polyisobutene.

GB-A 1 115 521 discloses, inter alia, the polymerization of isobuteneover a Na-X zeolite loaded with a platinum compound. This yieldsessentially dimers and trimers of isobutene along with minor amounts oftetramers and higher polymers. No information is given about themolecular weight of the higher polymers thus formed and their terminaldouble bond content.

The unpublished application PCT/EP 96/03441 discloses a process forpreparing low molecular weight, reactive and halogen-free polyisobuteneutilizing, as a catalyst, a support material comprising anoxygen-containing zirconium compound and doped with various promoters.

It is an object of the present invention to find a process for preparinghalogen-free, reactive polyisobutene having a terminal double bondcontent of more than 50 mol %, a terminal double bond and β-olefinicdouble bond content of more than 80 mol % and an average molecularweight of 280-10000 dalton using a heterogeneous catalyst. Anotherobject of the present invention is to find heterogeneous catalysts whichare suitable for this process and which make it possible to operate theprocess for preparing polyisobutene in an economical manner.

We have found that these objects are achieved by a process for preparinghalogen-free, reactive polyisobutene having a terminal double bondcontent of more than 50 mol % and an average molecular weight M_(n) of280-10000 dalton by the cationic polymerization in the liquid phase ofisobutene or hydrocarbon mixtures comprising isobutene, which comprisespolymerizing at from −30° C. to +40° C. in the presence of aheterogeneous polymerization catalyst comprising one or more oxides ofthe elements of transition groups Vb and VIb of the Periodic Table ofthe Elements or in the presence of a heterogeneous polymerizationcatalyst comprising one or more oxidic compounds of one or more elementsof transition groups Vh and VIh of the Periodic Table of the Elementssupported on a non-zeolitic oxidic support material which is not anoxygen-containing zirconium compound, the catalyst not containing atechnically effective amount of halogen.

In contrast to the undoped oxides of the individual support materialswhich are virtually inactive as catalysts for the polymerization ofisobutene or only have a very low catalytic activity, the catalysts tobe used according to the invention have a good or very good activity andselectivity for the polymerization of isobutene to give reactive, lowmolecular weight polyisobutene having a terminal double bond content ofmore than 50 mol % and an average molecular weight of 280-10000 dalton.Since it is not necessary to add halogenated compounds to the catalyststo be used according to the invention to achieve a high activity andselectivity, these catalysts provide an economical way to preparehalogen-free PIB.

Since both the method of preparing the catalysts to be used according tothe invention and the chemical and physical analytical data of thesecatalysts suggest that the support material present in these catalystsis in the form of oxidic compounds of the individual support components,use is being made in the present application, for simplicity, of theterms oxidic support material or individual oxides of these supportmaterials or the support components which constitute the supportmaterial. For the purposes of the present invention, zeolites ormaterials having zeolite-like properties, such as silicon aluminumphosphates (SAPOS), silicatic mesoporous materials or clays, such asbentonites, montmorillonites, kaolin, which are collectively “termedzeolitic materials” in the present application, are not regarded asoxidic support materials.

The polymerization catalysts used in the process of the invention areheterogeneous catalysts comprising, as catalytically active components,oxygen-containing compounds of one or more elements of transition groupVD and/or VIb of the Periodic Table of the Elements. The catalysts whichmay be used according to the invention can be subdivided into twocatalyst types. Catalysts of type (A) are unsupported catalysts, i.e.catalysts which are composed of oxides of one or more of the elements oftransition group Vb and/or VIb of the Periodic Table of the Elements andwhich contain no or virtually no support materials. The catalysts oftype (B) belong to the class of supported catalysts and comprise, ascatalytically active component(s), one or more oxidic compounds of oneor more elements of transition group Vb and/or VIb of the Periodic Tableof the Elements supported on an oxidic A; support material which is notan oxygen-containing zirconium compound, these supported catalysts notcontaining technically effective amounts of halogen. These catalyticallyactive components are also called promoters herein.

Advantageous catalysts of type (A) are the oxides of chromium,molybdenum, tungsten, vanadium, niobium or tantalum or mixtures of twoor more of these oxides, in the form of powders or shaped articles, suchas extrudates, spheres, rings or spirals. Preferred catalysts of type(A) are the oxides of chromium, molybdenum, tungsten and vanadium ormixtures of two or more of these oxides or mixtures of one or more ofthese oxides with niobium oxide (Nb₂O₅) or tantalum oxide (Ta₂O₅). Ofthe various oxides of different oxidation state which the elements oftransition groups V and VI may form, preference is given to usingchromium (IV) oxide (CrO₂), chromium (III) oxide (Cr₂O₃), molybdenum(VI) oxide (MoO₃), tungsten (VI) oxide (WO₃), vanadium pentoxide (V₂O₅),niobium pentoxide (Nb₂O₅) and tantalum pentoxide (Ta₂O₅) as catalystsfor the process of the invention. These oxides may be prepared in aconventional manner, for example by calcining in an oxygen-containingatmosphere of, for example, ammonium chromate ((NH₄)₂CrO₄), ammoniummolybdate ((NH₄)₂MoO₄), ammonium tungstate ((NH₄)₂WO₄), ammoniumvanadate (NH₄VO₃), ammonium niobate (NH₄NbO₃) or ammonium tantalate(NH₄TaO₃). As a result of this preparation method, the oxides thusobtained may also contain small amounts of oxides of lower or possiblyhigher oxidation states of these elements.

Oxidic support materials for the catalysts of type (B) are the solid,heat-resistant oxides of the elements of main groups IIb, IIIb and IVbof the Periodic Table of the Elements and of the Elements of transitiongroups I, II, III and IV (excluding zirconium), VII and VIII, theelements of transition group III including the rare earth metals. Aswill be described elsewhere herein in more detail, these oxides may bepresent in the support material, as a result of their preparation, inthe form of defined oxides of stoichiometric composition, in the form ofnon-stoichiometric oxidic compounds, in the form of mixed-valency oxidesor, when a support material comprising a plurality of elements of theabovementioned groups of the Periodic Table of the Elements are used, inthe form of mixed oxides of the relevant elements, in which case, againas a result of the preparation method, the support in question maycontain individual types of these oxide forms virtually exclusively, butalso different oxide forms simultaneously. For the purposes of thepresent application, heat-resistant oxides are those of theabovementioned oxide forms which are formed under the individualcalcination conditions used for the preparation of the individualcatalysts or are stable under these conditions.

Of the oxides of main group II of the Periodic Table of the Elements,for example, preference is given to using the oxides of beryllium,magnesium and calcium as support material. Preferred support materialsfrom main group III are the oxides of boron, aluminum and gallium.Suitable support materials from main group IV are the oxides of silicon,germanium, tin and lead, preference being given to the oxides of silicon(SiO₂), tin and lead, preferred support materials of the various oxidesof tin and lead being in particular tin dioxide (SnO₂), lead(II) oxide(PbO), lead dioxide (PbO₂) and minium (Pb₃O₄).

It is also possible to use the oxides of the elements of transitiongroup I of the Periodic Table of the Elements as support materials forthe catalysts which may be used according to the invention, butpreference is given to the oxides of copper and in particular copper(II) oxide (CuO). The preferred oxidic support material of transitiongroup II of the Periodic Table of the Elements is zinc oxide (ZnO).Suitable oxides of transition group IV of the Periodic Table of theElements for use as support materials are titanium dioxide (TiO₂) andhafnium dioxide (HfO₂), preference being given to titanium dioxide. Ofthe oxides of transition group VII of the Periodic Table of theElements, the oxides of manganese are preferably used as supportmaterial, particularly preferably manganese dioxide (MnO₂) and manganese(III) oxide (Mn₂O₃), and preferred support materials of the oxides ofthe elements of transition group VIII are the oxides of iron, nickel andcobalt, in particular the iron oxides Fe₂O₃ and Fe₃O₄.

All the oxides of the elements of transition group III of the PeriodicTable of the Elements including the rare earth metals can be usedadvantageously as support material for the catalysts which may be usedaccording to the invention, preference being given to scandium oxide(Sc₂O₃), yttrium oxide (Y₂O₃), lanthanum oxide (La₂O₃), cerium (III)oxide (Ce₂O₃), samarium (III) oxide (Sm₂O₃) and ytterbium oxide (Yb₂O₃).

Particularly preferred support materials of the catalysts to be usedaccording to the invention are boron trioxides, aluminum oxides,lanthanum oxides, titanium oxides, silicon dioxides, lead oxides andiron oxides including their various crystal modifications, in particulariron (III) oxide (Fe₂O₃) and SiO₂. It is also advantageous to usemixtures of two or more of these oxidic support materials as support forthe catalysts to be used according to the invention.

The supported catalysts to be used according to the invention can bemade in various ways by conventional methods, for example byimpregnating the support material with a solution, preferably an aqueoussolution, of a precursor compound for the relevant promoters), where, inthe case of doping the support with a plurality of promoters, thesepromoters may be applied to the support material simultaneously in oneimpregnating step or individually, successively, in a plurality ofimpregnating steps, by coprecipitation of the precursor compounds forthe support material and the promoter or by cosolvatation, i.e. bysimultaneous dissolution of these precursor compounds in a solvent,preferably water, and evaporation of the resulting solution, followed bydrying and calcining the resulting solids to give the catalysts whichmay be used according to the invention.

When the catalysts are prepared by impregnation, either theprefabricated support material, i.e. the relevant oxide or a mixture ofa plurality of the suitable oxides, or a precursor compound for thesupport material which is sparingly soluble in the relevant solvent andcan be converted into the support material by thermal treatment, e.g. ahydroxide, a carbonate, a nitrate or an organic salt of the supportcomponent, is impregnated with a solution, preferably an aqueoussolution, of a precursor compound for the relevant promoter(s) atgenerally from 20 to 80° C., the impregnated support material orprecursor compound for the support material is dried and the impregnatedand dried support material or its precursor compound is then calcined attemperatures at which the promoter precursor compound and, optionally,the precursor compound for the support material, is/are used, aredecomposed to give the catalytically active promoter or the oxidicsupport material, respectively, and the finished catalyst is formed.

When the catalysts of the invention are prepared by precipitation ofprecursor compounds for the support material and/of the promoter, aconventional precipitation method can be used. This generally involvesprecipitating solutions of water-soluble salts of the support componentand/or the promoter by addition of a precipitating agent. Examples ofprecipitating agents used are bases, such as alkali metal hydroxides andcarbonates or aqueous ammonia solutions, which form sparingly solublecompounds with the relevant salts of the support component. Preferredprecipitating agents are alkali metal carbonates. The choice of basedepends on the support component elements to be precipitated in eachparticular case. Depending on the type of support component to beprecipitated, it may be necessary to conduct the precipitation under apH control in a certain pH range, since some of the elements suitable assupport component have amphoteric properties and/or may form solublecomplex compounds with the precipitating agent. It will be appreciatedthat, depending on the type of support component or promoter precursorcompound to be precipitated, it is also possible to use otherprecipitating agents as the abovementioned bases, if the anions of theseprecipitating agents can form sparingly soluble compounds with therelevant elements of the support component or promoter precursorcompound. For example, it is possible to use solutions of water-solublesalts of elements of the support component, e.g. alkali metal silicatessuch as water glass or alkali metal borates such as borax, for theprecipitation of the relevant promoter precursor compound, it generallybeing advantageous to conduct such a precipitation in a certain pHrange. The resulting precipitates are advantageously separated from theliquid, washed until free from salt, dried and calcined.

It may also be advantageous to precipitate only the support component byone of the abovementioned methods in a precipitation reaction and to mixthe resulting precursor for the support material, e.g. with an oxide ora precursor compound for the promoter, followed by drying and subsequentcalcining to produce the catalyst. It is also possible to precipitatethe promoter precursor compound onto the support material initiallycharged in the precipitation vessel followed by workup of the resultingmaterial as described above to produce the catalyst. It is particularlyadvantageous to precipitate the precursor compounds for the supportmaterial and the promoter in separate precipitations, followed by mixingof the resulting precipitates, e.g. in a kneader or extruder, andconversion into the catalyst in a similar manner.

Instead of precipitating the catalysts to be used according to theinvention, they can also be produced by cosolvation of precursorcompounds for the support material and the promoter, evaporating offthis solution and drying and calcining of the resulting residue.

In addition to the above-described wet chemical methods, the promoterprecursor compounds may also be deposited on the support material or aprecursor compound for the support material, for example, by vapordeposition of the promoter elements or promoter element compounds or byflame-spraying. Calcination in an oxygen-containing atmosphere thengives the catalysts to be used according to the invention.

The catalyst precursors obtained by impregnation, precipitation orcosolvation are generally dried at from 50° C. to 300° C., preferably atfrom 60° C. to 200° C., particularly preferably at from 70° C. to 150°C. By drying under reduced pressure, it is possible to accelerate thedrying process or to use a drying temperature lower than the statedvalues.

The dried catalyst precursors or the catalyst precursors obtained byvapor deposition or flame-spraying are generally calcined in anoxidizing atmosphere, in particular in the presence of oxygen-containinggases, preferably in air. The calcination temperature is generally morethan 300° C. to 1000° C., preferably more than 300° C. to 800° C.,particularly preferably more than 300° C. to 700° C. Depending on thetype, preparation method and composition of the relevant catalystprecursor, the calcination time is generally from 1 to 20 hours.

During calcination in an oxidizing atmosphere, the dried catalystprecursors obtained by the preparation method used in the particularcase (impregnation, precipitation, cosolvatation, vapor deposition orflame-spraying) are converted into the catalysts, the precursorcompounds for the support material and/or the promoter contained thereinbeing thermally decomposed or oxidized to the corresponding oxidiccompounds. Examples of precursor compounds are thermally or oxidativelydecomposable salts, when the impregnation method is used, sparinglysoluble hydroxides, carbonates, basic salts, oxyhydroxides, silicates orborates, when the precipitation method is used, and the relevantoxidizable elements, when the vapor deposition method or theflame-spraying method is used. Depending on the type, composition andpreparation method of the catalyst precursor, the calcination conditionsused lead to the decomposition of thermally or oxidatively decomposablesalts, e.g. to give the relevant oxides, mixed-valency oxides and/ormixed oxides, to a conversion of the precipitates obtained byprecipitation and subsequent drying, e.g. into the relevantstoichiometric or non-stoichiometric oxidic compounds, mixed-valencyoxides and/or mixed oxides, and to the oxidation of the elementsdeposited on the support material or a support material precursor byvapor deposition to give the corresponding oxides. Consecutive reactionsmay also occur in the case of the calcination. These involve, forexample, the reaction of oxides initially formed from the promoterprecursor with the oxidic support material in a solid phase reaction togive mixed oxides or the conversion of relatively high oxidation statepromoter compounds or support components on the catalyst surface withrelatively low oxidation state promoter or support components present inthe interior of the catalyst particle in a solid phase reaction to givemixed-valency or non-stoichiometric oxides. Accordingly, depending onthe type and composition of the support and promoter components andtheir precursors, the preparation method of the catalyst precursor andthe calcination conditions used, individual types of the above-describedoxide forms may predominate over the other oxide forms in the finishedcatalyst, or various types of these oxide forms may be presentsimultaneously.

It will therefore be appreciated that the calcination conditions foreach individual catalyst must be chosen according to its composition,the manner in which the promoter elements have been deposited on thesupport material or its precursor and the type of the compounds of thepromoter elements used for this purpose, if optimum results are to beachieved in the process according to the invention. The individualchoice of these calcination conditions within the range of theabovementioned calcination temperatures and calcination time can beeasily made by a person skilled in the art by means of a few routineexperiments.

The above-described preparation methods for the catalysts are onlyillustrative and can be varied, if desired. Which one of theabovementioned methods for preparing the catalysts for type (B) is used,is generally not critical for the effectiveness of these atalysts in theprocess according to the invention. The choice of a particularpreparation method generally depends on the availability of particularstarting materials for the relevant promoters and support materials, theavailability of the equipment required for the operation methods, thecomposition of the desired catalysts and the chemical behavior knownfrom text books of the starting materials available for the preparationof the relevant catalysts under the conditions of the variouspreparation methods.

Apart from their elemental composition, the exact chemical structure ofthe catalysts to be used according to the invention is virtually unknownfor the abovementioned reasons. It is possible that the promoterelements from transition group V and/or VI of the Periodic Table of theElements and the oxidic support material form mixed oxides ormixed-valency oxides which form catalytically active centers and thuscatalyze the isobutene polymerization, but it is also possible that thepromoter elements are attached to the surface of the support material bychemical bonds, for example via oxygen linkages, and thus cause thecatalytic activity of the doped support materials which exhibitvirtually no catalytic activity in the process according to theinvention without such doping. It is therefore impossible to specify themode of action of these catalysts: when the acidity of the catalystswhich may be used according to the invention is determined by Hammetttitration, some prove to be strong acids using this method of titration,whereas others are virtually neutral but still catalyze the isobutenepolymerization resulting in the desired high terminal double bondcontent.

Since the exact chemical structure of the catalysts to be used accordingto the invention is unknown, the individual catalysts are characterizedby their support element and promoter element content in % by weight,calculated as the relevant support element or promoter element,respectively, based on the total weight of the calcined catalyst. Theremainder to 100% by weight is mainly contributed by the oxygen attachedto these elements, but also by technically ineffective impurities, e.g.alkali metal compounds, which have been incorporated into the catalystin the course of its preparation. The catalysts to be used according tothe invention may also contain, after their calcination, hydrogen inchemically bound form, e.g. in the form of OH groups or in the form ofwater of crystallization which cannot be removed even under calcinationconditions.

The molar ratio of the support element(s), calculated as the sum of therelevant support elements, to the promoter element present in thecatalyst or, cumulatively, to the promoter elements present in thecatalyst, in each case calculated as the corresponding element, supportelement/promoter element, is generally from 50:50 to 99.9:0.1,preferably from 54:46 to 99.7:0.3, particularly preferably from 80:20 to98:2. Alkali metals, which are usually present in the catalyst in theform of oxygen-containing alkali metal compounds, if at all, may bepresent in the catalyst as a result of its preparation in amounts of upto 1% by weight, e.g. from 0.1 to 1.0% by weight, in each casecalculated as alkali metal. The alkali metals may be introduced into thecatalyst, for example, by the use of alkali metal-containingprecipitating agents or by alkali metal impurities or constituents ofthe promoter element compounds used for promotion or the precursorcompounds used for preparing the support material.

The polymerization catalysts to be used according to the invention aregenerally and preferably halogen-free. However, depending on the mannerof their preparation, in particular depending on the halogen content ofthe raw materials used for their preparation, these catalysts may becontaminated with halogen in amounts which are technically unavoidablyintroduced by these raw materials, but are technically inefficient andneither exhibit a promoter effect nor lead to the formation ofhalogenated polyisobutene. The reason for the technical inefficiency ofsuch undesired halogen impurities in the catalysts to be used accordingto the invention is that these impurities are distributed unspecificallythroughout the catalyst and do not form a part of the catalyticallyactive centers. This is the difference between the catalysts to be usedaccording to the invention and, among others, the halogen-containingcatalysts according to U.S. Pat. No. 4,288,649 or U.S. Pat. No.5,326,920, in which halogens are incorporated into the catalyticallyactive centers of the catalyst in a controlled manner. The catalysts tobe used according to the invention contain technically unavoidablehalogen impurities in an amount of generally less than 1000 ppm byweight, preferably less than 100 ppm halogen by weight, in each casebased on the total weight of the calcined catalyst, particularpreference being given to using halogen-free catalysts.

Some of the catalysts to be used according to the invention are known,for example a few of the chromium on silicon dioxide catalysts describedin EP-A 535 516 which to date have only been used in processes for thepolymerization of ethylene.

Prior to use in the process according to the invention, the catalysts tobe used according to the invention are advantageously conditioned, i.e.they are shaped to give shaped articles such as tablets, spheres,cylinders, rings or spirals or comminuted to spall in a conventionalmanner and preferably used in this form in a fixed bed in the reactor ormilled to give a powder and used in this form, advantageously assuspension catalysts.

The catalysts to be used according to the invention can be stored over avirtually unlimited period of time, in particular with the exclusion ofmoisture. Catalysts which have become moist are advantageously driedunder atmospheric pressure or reduced pressure, under atmosphericpressure in general at temperatures above 150° C., preferably at 180 to300° C., under reduced pressure also at lower temperatures, prior touse.

The starter materials that may be used in the process of the inventionare both pure isobutene and hydrocarbon mixtures comprising isobutene,such as C₄ raffinate or isobutane/isobutene mixtures derived from thedehydrogenation of isobutane. C₄ raffinate refers to hydrocarbonmixtures obtained by substantial removal of 1,3-butadiene, i.e. removaldown to trace amounts, for example by extractive distillation, from theC₄ cut from steam crackers or fluid catalyzed crackers (cf. Weissermel,Arpe: Industrielle Organische Chemie, p. 69, 102-103, 2nd Ed., VerlagChemie 1978).

The process of the invention can be carried out batchwise orcontinuously at generally from −30° C. to +40° C., preferably from −25to +30° C., particularly preferably from −20° C. to +20° C., underatmospheric pressure or superatmospheric pressure, especially under theautogeneous pressure of the reaction system, so that the isobuteneremains in liquid form. It is possible to use conventional reactors suchas stirred reactors or loop reactors in batchwise operation of theprocess or loop reactors or reactor batteries in continuous operation ofthe process. It is also advantageous to use, in continuous operation ofthe process of the invention, tubular reactors or tubular reactorbatteries operated in upflow or downflow mode. It is possible for thecatalysts to be used according to the invention, preferably when usingloop reactors or tubular reactors, to be arranged in a fixed bed or tobe suspended in the reaction medium in powder form. The isobutenepolymerization can be carried out with or without preferably a polar,halogen-free solvent, preferably hydrocarbons. When hydrocarbon mixturescomprising isobutene are used as starting material, the hydrocarbonswhich are present therein in addition to the isobutene act as solventsor diluents. Because of the exothermic nature of the isobutenepolymerization, it may be advantageous to provide the reactors used withinternal or external cooling means.

The desired average molecular weight M_(n) of the polyisobutene can beadjusted by varying the reaction parameters in the process of theinvention.

In the batch process, the average molecular weight M_(n) is generallyadjusted by variation of the amount of catalyst used, the reaction timeand the reaction temperature. Depending on the amount of catalyst used,the reaction time is generally from 0.01 to 10 hours, preferably from0.1 to 8 hours. In the discontinuous embodiment of the process of theinvention, the catalyst is generally added in an amount of 0.1-50% byweight, preferably 0.5-20% by weight, particularly preferably 1-10% byweight, in each case based on the weight of the isobutene present in thestarting material used. Depending on the catalyst and starting materialused, the optimum polymerization conditions for the preparation ofpolyisobutene having a desired average molecular weight M_(n) areadvantageously determined in preliminary experiments. In continuousoperation of the process of the invention, the average molecular weightM_(n) is adjusted correspondingly, but here the reaction parameters ofspace velocity and residence time are varied instead of the amount ofcatalyst used.

The isolation of the polyisobutene from the polymerization mixturegenerally does not include any special technical features and may beeffected by distillation, which, when a suspended catalyst is used, ispreceded by the removal of the suspended catalyst, for example byfiltration, centrifugation or decanting. The distillation advantageouslyinitially removes from the polyisobutene volatile components of thepolymerization mixture such as unconverted isobutene, hydrocarbonspresent in the starting material or added as solvents and thenhigher-boiling byproducts, for example low molecular weight isobuteneoligomers.

The process of the invention provides an economical way to preparereactive, halogen-free polyisobutene having an average molecular weightM_(n) of generally 280-10000 dalton, preferably 400-6000 dalton,particularly preferably 500-5000 dalton, and a terminal double bondcontent of more than 50 mol %.

EXAMPLES

I. Catalyst Preparation

Catalysts A-L were prepared and used in powder form.

The Mo, W, Si, Pb, La, Fe and V contents of each catalyst weredetermined by X-ray fluorescence analysis (Lit. R. Bock: Methoden derAnalytischen Chemie; Vol. 2: Nachweis- und Bestimmungsmethoden Teile 1,Verlag Chemie, Weinheim 1980), the B, Cr and Ti contents of eachcatalyst were determined by ICP (Inductively Coupled Plasma)-atomemission spectroscopy (Lit. A. Montaser; D. W. Golightly: InductivelyCoupled Plasmas in Analytical Atomic Spectrometry; 2nd Ed., VCHVerlagsgesellschaft, Weinheim), the Cl and S contents of each catalystwere determined by the Schbniger method and by combustion analysis(Lit.: F. Ehrenberger: Quantitative organische Elementaranalyse; VCHVerlagsgesellschaft, Weinheim 1991). Prior to the analysis for theseelements, the calcined catalysts were again dried until a constantweight was obtained and immediately analyzed in this form.

Catalyst A: 50 g of ammonium heptamolybdate tetrahydrate((NH₄)₆Mo₇O₂₄·4H₂O) was calcined in air at 500° C. for 5 h. Aftercalcination, the catalyst had an Mo content of 66.0% by weight.

Catalyst B: 50 g of SiO₂ (Aerosile 200 from Degussa, Hanau) were placedin a 1 l flask and mixed with a solution consisting of 51.42 g ofammonium heptamolybdate tetrahydrate ((NH₄)₆Mo₇O₂₄·4H₂O) and 700 ml ofwater. The suspension was rotated on a rotary evaporator for 30 min.Excess water was then removed at 60° C. The resulting material waspredried at 150° C. for 16 h and calcined in air at 500° C. for 16 h.After calcination, the catalyst had the following Mo and Si contents:

Mo: 26.0% by weight

Si: 28.5% by weight

Catalyst C: A mixture of 39 g of (NH₄)₆Mo₇O₂₄·4H₂O in 100 g of water and142 g of FeOOH was kneaded for 90 min and then dried at 120° C. for 12h. The material was then milled and then calcined at 500° C. for 2 h.After calcination, the catalyst had the following Mo and Fe contents:

Mo: 13.6% by weight

Fe: 54.0% by weight

Catalyst D: 50 g of Pb(NO₃)₂ were placed in a 1 1 flask and mixed with asolution consisting of 37.31 g (NH₄)₆Mo₇O₂₄·44H₂O and 250 ml of water.The suspension was rotated on a rotary evaporator for 30 min. Excessivewater was then removed at 60° C. The resulting material was predried at150° C. for 16 h and calcined in air at 500° C. for 16 h. Aftercalcination, the catalyst had the following Mo and Pb contents:

Mo: 31.5% by weight

Pb: 49.0% by weight

Catalyst E: 88.3 g of a (NO₃)₃·6H₂O were placed in a 1 l flask and mixedwith a solution consisting of 12.6 g of (NH₄)₆Mo₇O₂₄·4H₂O and 400 ml ofwater. The suspension was rotated on a rotary evaporator for 30 min.Excess water was then removed at 60° C. The resulting material waspredried at 150° C. for 16 h and calcined in air at 500° C. for 16 h.After calcination, the catalyst had the following Mo and La contents:

Mo: 17.7% by weight

La: 47.5% by weight

Catalyst F: 50 g of boric acid were placed in a 1 l flask and mixed witha solution consisting of 199.88 g of ammonium heptamolybdatetetrahydrate ((NH₄)₆Mo₇O₂₄·4H₂O) and 600 ml of water. The suspension wasrotated on a rotary evaporator for 30 min. The material was thenpredried and calcined in air at 500° C. for 16 h. After calcination, thecatalyst had the following Mo and B contents:

Mo: 55.0% by weight

B: 4.1% by weight

Catalyst G: 50 g of iron (II) sulfate heptahydrate were placed in a 1 lflask and mixed with a solution consisting of 2.83 g of VCl₃ and 250 mlof water. The solution was rotated on a rotary evaporator for 30 min.Excess water was then removed at 60° C. The resulting material waspredried at 150° C. for 16 h and calcined in air at 500° C. for 16 h.After calcination, the catalyst had the following Fe, V, Cl and Scontents:

Fe: 29.8% by weight

V: 5.4% by weight

Cl: 0.001% by weight

S: 16.0% by weight

Catalyst H: A mixture of 20 g of tungstic acid (H₂WO₄) in 80 g of 32%strength NH₃ solution was kneaded together with 84 g of FeOOH for 90min. and then dried at 120° C. for 12 h. The material was milled andcalcined at 300° C. for 2 h. After calcination, the catalyst had thefollowing W and Fe contents:

W: 15.5% by weight

Fe: 56.0% by weight

Catalyst I: 150 g of titanium dioxide were kneaded together with 37.5 gof CrO₂ in 160 g of water for 120 min. and then dried at 120° C. for 12h. The material was milled and then calcined first at 350° C. for 2 hand then at 650° C. for 2 h. After calcination, the catalyst had thefollowing Cr and Ti contents:

Cr: 13.2% by weight

Ti: 46.0% by weight

Catalyst J: 120 g of Ti(OH)₄ were homogenized together with 16.8 g ofmolybdic acid H₂MoO₄ and 100 ml of water in a kneader, dried at 100° C.and calcined in air at 500° C. for 5 h. After calcination, the catalystcontained:

Mo: 10.0% by weight

Ti: 51.0% by weight

Catalyst K: 120 g of Ti(OH)₄ were homogenized together with 15.3 g ofH₂WO₄ and 100 ml of water in a kneader, dried at 110° C. and calcined inair at 700° C. for 5 h. After calcination, the catalyst contained:

W: 12.0% by weight

Ti: 51.0% by weight

Catalyst L:

120 g of Ti(OH)₄ were homogenized together with 94.1 g of aqueousvanadium oxalate solution (V content: 5 mol % calculated as V₂O₅) and 20ml of water in a kneader, dried at 110° C. and calcined at 500° C. for 5h. After calcination, the catalyst had the following Ti and V contents:

Ti: 52.0% by weight

V: 7.7% by weight

II. Polymerization of Isobutene

The number average molecular weight M_(n) which is also referred toherein as average molecular weight M_(n) was determined by gelpermeation chromatography (GPC) using standardized polyisobutenes forcalibration. The number average molecular weight M_(n) was calculatedfrom the GPC chromatograms obtained using the equation

M _(n) =Σc _(i)/Σ(c _(i) /M _(i))

where c_(i) is the concentration of the individual polymer species inthe resulting polymer mixture and M_(i) is the molecular weight of theindividual polymer species i. The molecular weight distribution, alsocalled dispersity (D), was calculated from the ratio of the averagemolecular weight (M_(w)) and number average molecular weight (M_(n))using the equation

D=M _(w) /M _(w) /M _(n)

where the weight average molecular weight M. was determined from the GPCchromatograms obtained using the equation:

M _(w) =Σc _(i) M _(i) /Σc _(i)

The α- and β-olefin contents (Formula I and II) were determined by¹³C-NMR spectroscopy.

In the ¹³C-NMR spectrum, the C atoms of the terminal double bond of theα-olefins I show peaks at a chemical shift of 114.4 ppm (CH₂) and 143.6ppm (C), whereas the signals of the C atoms of the trisubstituted doublebond of the β-olefins II are at 127.9 (=CH-R) and 135.4 ppm (=C(CH₃)₂).The α- and β-olefin contents can be determined by evaluation of the peakareas and by comparison with the peak areas of the other olefinic Catoms. Deuterated chloroform (CDCl₃) was used as solvent andtetramethylsilane was used as internal standard.

Example 1

10 g of isobutene were condensed into a 25 ml glass pressure vesselunder argon at −70° C. 1 g of catalyst A which had been predried at 180°C./0.3 mbar was added, the vessel was sealed and the suspension wasstirred at 0° C. for 2 h under the autogeneous pressure of the reactionsystem. The polymerization mixture was then diluted with 10 g ofn-hexane at 0° C. Unconverted isobutene was evaporated at roomtemperature, the catalyst was filtered off and the solvent added wasremoved from the filtrate by distillation at room temperature, slowlyreducing the pressure to 0.3 mbar. Low molecular weight isobuteneoligomers were removed from the resulting polyisobutene by Kugelrohrdistillation at 120° C./0.3 mbar. The colourless polyisobutene which wasobtained in a yield of 11% had an average molecular weight M_(n) of 3640dalton, a molecular weight distribution D of 3.4 and a terminal doublebond content (=α-olefin content) of 75 mol %. The β-olefin content was26 mol %.

Examples 2 to 12

Examples 2 to 12 were carried out as described in Example 1. Table 1summarizes the results of these batchwise runs obtained using thevarious catalysts and different amounts of catalysts.

Table 1: Batch polymerization of isobutene polymerization conditions:polymerization temperature: 0° C.; Autogeneous pressure; polymerizationtime: 2 h; amount used: 10 g of isobutene

Amount of Ex. Cata- catalyst Yield ¹⁾ S (I) ²⁾ S (I + II) ³⁾ No. lyst[g] [%] [mol %] [mol %] M_(n) D 2 B 0.6 13 76 86 2231 3.6 3 C 2.0 8 7487 447 1.3 4 D 1.0 18 73 94 4246 2.2 5 E 1.0 3 65 85 5110 8.4 6 F 1.0 1056 82 5294 2.5 7 G 1.4 5 78 91 1073 1.6 8 H 1.0 14 67 80 450 3.9 9 I 1.55 51 76 706 6.1 10 J 0.2 12 73 80 625 2.5 11 K 0.2 13 78 86 884 5.7 12 L0.5 8 83 90 1126 4.6 ¹⁾ Evaporation residue after Kugelrohr distillation(120° C./0.3 mbar), based on isobutene used ²⁾ S (I) = Terminal doublebond content = α-olefin content ³⁾ S (I + II) = Terminal double bondcontent + β-olefinic double bond content.

We claim:
 1. A process for preparing a halogen-free, reactivepolyisobutene having a terminal double bond content of more than 50 mol% and an average molecular weight M_(n) of 280-10000 dalton whichcomprises: carrying out a cationic polymerization of isobutene in aliquid phase consisting essentially of isobutene or mixtures thereofwith a liquid hydrocarbon at a temperature of from −30° C. to 40° C. inthe presence of at least one heterogeneous polymerization catalyst whichis substantially free of halogen and is selected from the groupconsisting of the oxides of the transition elements of Groups V and VIof the Periodic Table of Elements, said catalyst being unsupported oroptionally supported on one or more compounds which are non-zeoliticoxides of at least one metal selected from the group consisting of theelements of the main Groups II, III and IV and also the transitionmetals of Groups I, II, III, IV, VII and VIII of the Periodic Table ofElements, but excluding all oxygen-containing zirconium compounds.
 2. Aprocess as claimed in claim 1, wherein the catalyst is carried on atleast one oxidic support.
 3. A process as claimed in claim 2, whereinthe catalyst is supported on a carrier selected from the groupconsisting of the oxides of silicon, titanium, iron, boron, lanthanum,lead or mixtures thereof.
 4. A process as claimed in claim 2, whereinthe catalyst is supported on a carrier selected from the groupconsisting of the oxides of silicon, titanium and iron or mixturesthereof.
 5. A process as claimed in claim 4, wherein the catalystconsists of molybdenum, titanium or mixtures thereof.
 6. A process asclaimed in claim 1, wherein the catalyst consists essentially of anunsupported metal oxide selected from the group consisting of the oxidesof vanadium, chromium, molybdenum and tungsten and mixtures thereof. 7.Of A process as claimed in claim 6, wherein the catalyst is selectedfrom the group consisting of the oxides of molybdenum, tungsten andmixtures thereof.